The present invention generally relates to semiconductor devices, and more particularly, to replacement metal gate (RMG) in bipolar complementary metal-oxide-semiconductor (BiCMOS) devices.
As integrated circuits continue to scale downward in size, fin field effect transistors (FinFETs) or tri-gate structures are becoming more widely used, primarily because FinFETs offer better performance than planar FETs at the same power budget. FinFETs are three dimensional (3-D), fully depleted metal-oxide semiconductor field effect transistor (MOSFET) devices representing an important part of advanced complementary metal-oxide semiconductor (CMOS) fabrication technology to create ever decreasing microelectronic devices.
FinFETs have a fin structure formed from the semiconductor substrate material extending between the device source and drain enfolding a channel region forming the bulk of the semiconductor device. The gate structure is located over the fins covering the channel region. Such architecture allows for a more precise control of the conducting channel by the gate, significantly reducing the amount of current leakage when the device is in off state.
CMOS devices, including FinFETs, may be combined with bipolar junction transistor (BJT) devices in bipolar complementary metal-oxide-semiconductor (BiCMOS) integrated circuits, which take advantage of the positive characteristics of both transistor types in the construction of the integrated circuit.
Bipolar junction transistor (BJT) technology may be typically found in demanding types of integrated circuits, especially integrated circuits for high-frequency applications. One high-frequency application for BJTs is in radiofrequency integrated circuits (RFICs), which are used in wireless communications systems, power amplifiers in cellular telephones, and other types of high speed integrated circuits. Conventional BJTs are three-terminal electronic devices that include three semiconductor regions, namely an emitter, a base, and a collector. Generally, a BJT includes a pair of p-n junctions, namely a collector-base junction and an emitter-base junction. A voltage applied across the emitter-base junction of a BJT controls the movement of charge carriers that produce charge flow between the collector and emitter regions of the BJT.
An NPN bipolar junction transistor includes two regions of N-type semiconductor material constituting the emitter-collector region, and a region of P-type semiconductor material located between the two regions of N-type semiconductor material constituting the base region of a NPN BJT device. A PNP bipolar junction transistor has two regions of P-type semiconductor material constituting the emitter-collector region, and a region of N-type semiconductor material located between the two regions of P-type semiconductor material constituting the base region of a PNP BJT device.
Scaling down of FETs dimensions requires a high-k metal gate to reduce gate leakage and improve device performance. A polycrystalline silicon material, commonly referred as polysilicon or poly, is normally used in the gate manufacturing process. Polysilicon exhibits high thermal resistivity, which makes a polysilicon gate resistant to high temperature processes such as high temperature annealing. The replacement of a polysilicon gate with a metal gate electrode is frequently used in advanced FinFET CMOS technology to address problems related to high temperature processing on metal materials. This process is known as replacement metal gate (RMG) or gate last process. A RMG process includes the formation of a dummy polysilicon gate structure, commonly referred to as a dummy poly gate or simply a dummy gate, enfolding the device fins. The device manufacturing may continue until deposition of an interlayer dielectric (ILD) layer. After the ILD layer deposition, the dummy gate may be removed and replaced with a high-k metal gate.